523 research outputs found
The detection efficiency of on-axis short gamma ray burst optical afterglows triggered by aLIGO/Virgo
Assuming neutron star (NS) or neutron star/stellar-mass black hole (BH)
mergers as progenitors of the short gamma ray bursts, we derive and demonstrate
a simple analysis tool for modelling the efficiency of recovering on-axis
optical afterglows triggered by a candidate gravitational wave event detected
by the Advanced LIGO and Virgo network. The coincident detection efficiency has
been evaluated for different classes of operating telescopes using observations
of gamma ray bursts. We show how the efficiency depends on the luminosity
distribution of the optical afterglows, the telescope features, and the sky
localisation of gravitational wave triggers. We estimate a plausible optical
afterglow and gravitational wave coincidence rate of 1 yr (0.1
yr) for NS-NS (NS-BH), and how this rate is scaled down in detection
efficiency by the time it takes to image the gravitational wave sky
localization and the limiting magnitude of the telescopes. For NS-NS (NS-BH) we
find maximum detection efficiencies of when the total imaging time is
less than 200 min (80 min) and the limiting magnitude fainter than 20 (21). We
show that relatively small telescopes can achieve similar detection
efficiencies to meter class facilities with similar fields of view,
only if the less sensitive instruments can respond to the trigger and image the
field within 10-15 min. The inclusion of LIGO India into the gravitational wave
observatory network will significantly reduce imaging time for telescopes with
limiting magnitudes but with modest fields of view. An optimal
coincidence search requires a global network of sensitive and fast response
wide field instruments that could effectively image relatively large
gravitational-wave sky localisations and produce transient candidates for
further photometric and spectroscopic follow-up.Comment: 6 pages, 2 figures, version 2, reference added typo correction,
Accepted by MNRA
Nuclear Equation of State from Observations of Short Gamma-Ray Burst Remnants
The favoured progenitor model for short -ray bursts (SGRBs) is the
merger of two neutron stars that triggers an explosion with a burst of
collimated -rays. Following the initial prompt emission, some SGRBs
exhibit a plateau phase in their -ray light curves that indicates additional
energy injection from a central engine, believed to be a rapidly rotating,
highly magnetised neutron star. The collapse of this `protomagnetar' to a black
hole is likely to be responsible for a steep decay in -ray flux observed at
the end of the plateau. In this letter, we show that these observations can be
used to effectively constrain the equation of state of dense matter. In
particular, we show that the known distribution of masses in binary neutron
star systems, together with fits to the -ray light curves, provide
constraints that exclude the softest and stiffest plausible equations of state.
We further illustrate how a future gravitational wave observation with Advanced
LIGO/Virgo can place tight constraints on the equation of state, by adding into
the picture a measurement of the chirp mass of the SGRB progenitor.Comment: accepted for publication in Phys. Rev.
Dopamine D_2-receptor activation elicits akinesia, rigidity, catalepsy, and tremor in mice expressing hypersensitive 4 nicotinic receptors via a cholinergic-dependent mechanism
Recent studies suggest that high-affinity neuronal nicotinic acetylcholine receptors (nAChRs) containing α4 and ÎČ2 subunits (α4ÎČ2*) functionally interact with G-protein-coupled dopamine (DA) D_2 receptors in basal ganglia. We hypothesized that if a functional interaction between these receptors exists, then mice expressing an M2 point mutation (Leu9'Ala) rendering 4 nAChRs hypersensitive to ACh may exhibit altered sensitivity to a D_2-receptor agonist. When challenged with the D_(2)R agonist, quinpirole (0.5â10 mg/kg), Leu9'Ala mice, but not wild-type (WT) littermates, developed severe, reversible motor impairment characterized by rigidity, catalepsy, akinesia, and tremor. While striatal DA tissue content, baseline release, and quinpirole-induced DA depletion did not differ between Leu9'Ala and WT mice, quinpirole dramatically increased activity of cholinergic striatal interneurons only in mutant animals, as measured by increased c-Fos expression in choline acetyltransferase (ChAT)-positive interneurons. Highlighting the importance of the cholinergic system in this mouse model, inhibiting the effects of ACh by blocking muscarinic receptors, or by selectively activating hypersensitive nAChRs with nicotine, rescued motor symptoms. This novel mouse model mimics the imbalance between striatal DA/ACh function associated with severe motor impairment in disorders such as Parkinsonâs disease, and the data suggest that a D_(2)Râα4*-nAChR functional interaction regulates cholinergic interneuron activity.âZhao-Shea, R., Cohen, B. N., Just, H., McClure-Begley, T., Whiteaker, P., Grady, S. R., Salminen, O., Gardner, P. D., Lester, H. A., Tapper, A. R. Dopamine D2-receptor activation elicits akinesia, rigidity, catalepsy, and tremor in mice expressing hypersensitive α4 nicotinic receptors via a cholinergic-dependent mechanism
Model sensitivity of the Weddell and Ross seas, Antarctica, to vertical mixing and freshwater forcing
We examine the sensitivity of the Weddell and Ross seas to vertical mixing and surface freshwater forcing using an oceanâsea ice model. The high latitude Southern Ocean is very weakly stratified, with a winter salinity difference across the pycnocline of only ?0.2 PSU. We find that insufficient vertical mixing, freshwater supply from the Antarctic Ice Sheet, or initial sea ice causes a high salinity bias in the mixed layer which erodes the stratification and causes excessive deep convection. This leads to vertical homogenisation of the Weddell and Ross seas, opening of polynyas in the sea ice and unrealistic spin-up of the subpolar gyres and Antarctic Circumpolar Current. The model freshwater budget shows that a ?30% error in any component can destratify the ocean in about a decade. We find that freshwater forcing in the model should be sufficient along the Antarctic coastline to balance a salinity bias caused by dense coastal water that is unable to sink to the deep ocean. We also show that a low initial sea ice area introduces a salinity bias in the marginal ice zone. We demonstrate that vertical mixing, freshwater forcing and initial sea ice conditions need to be constrained simultaneously to reproduce the Southern Ocean hydrography, circulation and sea ice in a model. As an example, insufficient vertical mixing will cause excessive convection in the Weddell and Ross seas even in the presence of large surface freshwater forcing and initial sea ice cover
The Middle Way: East Asian masters studentsâ perceptions of critical argumentation in U.K. universities.
The paper explores the learning experiences of East Asian masters students in dealing with Western academic norms of critical thinking in classroom debate and assignment writing. The research takes a cultural approach, and employs grounded theory and case study methodology, the aims being for students to explain their perceptions of their personal learning journeys. The data suggest that the majority of students interviewed rejected full academic acculturation into Western norms of argumentation. They instead opted for a âMiddle Wayâ that synergizes the traditional cultural academic values held by many East Asian students with those elements of Western academic norms that are perceived to be aligned with these. This is a relatively new area of research which represents a challenge for British lecturers and students
âIt Takes Two Hands to Clapâ: How Gaddi Shepherds in the Indian Himalayas Negotiate Access to Grazing
This article examines the effects of state intervention on the workings of informal institutions that coordinate the communal use and management of natural resources. Specifically it focuses on the case of the nomadic Gaddi
shepherds and official attempts to regulate their access to grazing pastures in the Indian Himalayas. It is often predicted that the increased presence of the modern state critically undermines locally appropriate and community-based resource management arrangements. Drawing on the work of Pauline Peters and Francis Cleaver, I identify key instances of socially embedded âcommonâ management institutions and explain the evolution of these arrangements
through dynamic interactions between individuals, communities and the agents of the state. Through describing the âliving spaceâ of Gaddi shepherds across the annual cycle of nomadic migration with their flocks I explore the
ways in which they have been able to creatively reinterpret external interventions, and suggest how contemporary arrangements for accessing pasture at different moments of the annual cycle involve complex combinations of the
formal and the informal, the âtraditionalâ and the âmodernâ
The NOD2-Smoking Interaction in Crohn's Disease is likely Specific to the 1007fs Mutation and may be Explained by Age at Diagnosis:A Meta-Analysis and Case-Only Study
Background: NOD2 and smoking are risk factors for Crohn's disease. We meta-analyzed NOD2-smoking interactions in Crohn's disease (Phase 1), then explored the effect of age at diagnosis on NOD2-smoking interactions (Phase 2).
Methods: Phase 1: MEDLINE and EMBASE were searched for studies (n = 18) providing data on NOD2 and smoking in Crohn's disease. NOD2-smoking interactions were estimated using odds ratios (ORs) and 95% confidence intervals (CIs) calculated using random effects models. Phase 2: A case-only study compared the proportion of smokers and carriers of the 1007 fs variant across ages at diagnosis (â€16, 17â40, >40 years).
Findings: Phase 1: Having ever smoked was less common among carriers of the 1007 fs variant of NOD2 (OR 0.74, 95%CI:0.66â0.83). There was no interaction between smoking and the G908R (OR 0.96, 95%CI:0.82â1.13) or the R702W variant (OR 0.89, 95%CI:0.76â1.05). Phase 2: The proportion of patients (n = 627) carrying the 1007 fs variant decreased with age at diagnosis (â€16 years: 15%; 17â40: 12%; >40: 3%; p = 0.003). Smoking was more common in older patients (â€16 years: 4%; 17â40: 48%; >40: 71%; p < 0.001).
Interpretation: The negative NOD2-smoking interaction in Crohn's disease is specific to the 1007Â fs variant. However, opposing rates of this variant and smoking across age at diagnosis may explain this negative interaction
VAST: An ASKAP Survey for Variables and Slow Transients
The Australian Square Kilometre Array Pathfinder (ASKAP) will give us an
unprecedented opportunity to investigate the transient sky at radio
wavelengths. In this paper we present VAST, an ASKAP survey for Variables and
Slow Transients. VAST will exploit the wide-field survey capabilities of ASKAP
to enable the discovery and investigation of variable and transient phenomena
from the local to the cosmological, including flare stars, intermittent
pulsars, X-ray binaries, magnetars, extreme scattering events, interstellar
scintillation, radio supernovae and orphan afterglows of gamma ray bursts. In
addition, it will allow us to probe unexplored regions of parameter space where
new classes of transient sources may be detected. In this paper we review the
known radio transient and variable populations and the current results from
blind radio surveys. We outline a comprehensive program based on a multi-tiered
survey strategy to characterise the radio transient sky through detection and
monitoring of transient and variable sources on the ASKAP imaging timescales of
five seconds and greater. We also present an analysis of the expected source
populations that we will be able to detect with VAST.Comment: 29 pages, 8 figures. Submitted for publication in Pub. Astron. Soc.
Australi
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